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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Thermocouples work on the Seebeck principle, discovered accidentally in 1822 by an Estonian physician named Thomas Seebeck. Basically, the Seebeck principle explains how two dissimilar metals generate a temperature-dependent flow of current at their welded junction when attached to a closed circuit.

Seebeck discovered that a compass needle would be deflected when a closed loop was formed of two metals joined in two places with a temperature difference between the junctions. The metals respond to temperature by assuming different voltage potentials, thereby generating a current related to the temperature of the junction.

This table lists the properties of the most common thermocouple junctions.

Type Metals ASTM


EMF (mV)

Over Temp Range



B Platinum30% Rhodium (+)

Platinum 6% Rhodium (-)



0 to 13.820 0 to 1700°C

(32 to 3092°F)

C W5Re Tungsten 5% Rhenium (+)

W26Re Tungsten 26% Rhenium (-)



0 to 37.066 0 to 2320°C

(32 to 4208°F)

E Chromel (+)

Constantan (-)



-9.835 to 76.373 -200 to 900°C

(-328 to 1652°F)

G Tungsten 26% (+)

Rhenium W-26% (-)



0 to 38.564 0 to 2320°C

(32 to 4208°F)

J Iron (+)

Constantan (-)



-8.095 to 69.553 0 to 750°C

(32 to 1382°F)

K Chromel (+)

Alumel (-)



-6.458 to 54.886 -200 to 1250°C

(-328 to 2282°F)

N Nicrosil (+)

Nisil (-)



-4.345 to 47.513 270 to 1300°C

(-450 to 2372°F)

R Platinum 13% Rhodium (+)

Platinum (-)



-0.226 to 21.101 0 to 1450°C

(32 to 2642°F)

S Platinum 10% Rhodium (+)

Platinum (-)



-0.236 to 18.693 0 to 1450°C

(32 to 2642°F)

T Copper (+)

Constantan (-)



-6.528 to 20.872 -200 to 350°C

(-328 to 662°F)

Thermocouple types R, S, and B are constructed of platinum and rhodium, and are referred to as noble metal thermocouples. They are more accurate and more stable than base metal types, but are more expensive.

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